This invention relates generally to a novel seam tracker apparatus. More particularly, this invention is a seam tracker apparatus including a novel and improved means of biasing the seam tracker probe to a selected mechanical null position, and a novel and improved means of detecting the variation of the seam tracker probe from an electrical null position.
In the past, it has been common to employ seam trackers which contain a probe which is disposed in a seam or joint to be welded and which responds to displacement of the seam tracker probe in either of two directions, horizontally, or vertically. As is known, this is done as the seam tracker probe moves, for example, within the seam or in abutment to the joint being welded, in order that the seam tracker apparatus may produce an output signal representative of the change of the position of the probe, horizontally or vertically. This output signal (or signals) is employed to modify accordingly the change of position of the welding head such that the welding head remains properly oriented with the seam or joint to ensure proper welding. While such arrangements have exhibited at least a degree of utility in maintaining the welding head in its proper orientation, room for a significant improvement remains.
A welding apparatus containing a seam tracker generally of the type disclosed in the present application is shown in the patent to Cecil et al., U.S. Pat. No. 3,997,757, issued on Dec. 14, 1976. The seam tracker disclosed therein contains a probe which is connected to a shaft extending through a generally cylindrical seam tracker housing (as disclosed to be of a type illustrated in the patent to Morehead, U.S. Pat. No. 3,171,012). The null point of the probe in the Morehead patent, as described in the Cecil patent is along the longitudinal axis of the seam tracker housing. The means for biasing the shaft to the null point consists of a flange on the shaft which is urged against a seat by a coiled spring disposed between the shaft flange and a collar mounted on the interior portion of the housing. Such an arrangement contains problems both in ensuring that the shaft is urged back to its proper null position (which is both a mechanical and electrical null position) when pressure is removed from the probe, and also in allowing slippage of the flange on a seating collar, such that excessive pressure on the probe may distort the orientation of the flange to the seating collar and produce an improper position of the other end of the shaft which contains a means for sensing the position of that other end of the shaft in order to determine the location of the probe with respect to the null position. Moreover, the pressure of the coil spring at various points around the circumference of the portion of the coiled spring abutting the flange will tend to be irregular, so that return to the null point or urging of the shaft back toward the null point as the position of the seam changes may not be totally accurate. Thus, improper indications of the exact position of the probe with respect to the null position may result.
In addition, the means for determining the position of the other end of the shaft with respect to the null position as shown in the Cecil patent is a pair or orthogonally oriented magnets associated with, respectively, a Hall effect generator. This arrangement, and particularly the use of bar magnets, as the position indicating elements, which bar magnets move in curved paths with respect to the respective stationary Hall effect generators results in certain inaccuracies which the applicants have endeavored to eliminate.
The problems enumerated in the foregoing are not intended to be exhaustive, but rather are among many which tend to impair the effectiveness of previously known seam trackers. Other noteworthy problems may also exist; however, those presented should be sufficient to indicate that seam trackers appearing in the prior art have not been altogether satisfactory.